Patas monkeys shown to be asymptomatic chronic carriers of Simian hemorrhagic fever (SHF) virus were superinfected with an acute strain of SHF virus (LVR or P-180 strains). Superinfection caused elimination of both the persistent and acute viruses, thus clearing the persistent infection. Although the persistent and acute virus strains are antigenically related, they are not identical as specific antisera do not have cross-neutralizing activity. Low titers of antibody were induced in patas monkeys infected with the persistent virus strain, while high titers were induced by the acute strains. These results suggest that the normal antibody response is suppressed in persistently infected patas monkeys and that this suppression can be reversed by superinfecting these animals with an acute strain of SHF virus. Virion polypeptides of three isolates of SHF virus were studied by slab polyacrylamide gel electrophoresis. All three isolates contained 5 virion polypeptides of similar molecular weight ranging from about 10K to 50K daltons. The largest polypeptide was a glycoprotein.